This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. This study is looking at the relationship between postpartum use of progestin-only birth control pills vs. combined birth control pills and the outcomes of breastfeeding continuation, infant growth, birth control method continuation, and pregnancy rates in breastfeeding women.